UnfinishedPrepare
			"$source_table.$source_primary_id_column IN ($source_ids_placeholder)",
			$source_ids
		);
	}

	/**
	 * Verify data from both source and destination tables and check if they were migrated properly.
	 *
	 * @param array $collected_data Collected data in array format, should be in same structure as returned from query in `$this->build_verification_query`.
	 *
	 * @return array Array of failed IDs if any, along with columns/meta_key names.
	 */
	protected function verify_data( $collected_data ) {
		$failed_ids = array();
		foreach ( $collected_data as $row ) {
			$failed_ids = $this->verify_entity_columns( $row, $failed_ids );
			$failed_ids = $this->verify_meta_columns( $row, $failed_ids );
		}

		return $failed_ids;
	}

	/**
	 * Helper method to verify and compare core columns.
	 *
	 * @param array $row        Both migrated and source data for a single row.
	 * @param array $failed_ids Array of failed IDs.
	 *
	 * @return array Array of failed IDs if any, along with columns/meta_key names.
	 */
	private function verify_entity_columns( $row, $failed_ids ) {
		$primary_key_column = "{$this->schema_config['source']['entity']['table_name']}_{$this->schema_config['source']['entity']['primary_key']}";
		foreach ( $this->core_column_mapping as $column_name => $schema ) {
			$source_alias      = "{$this->schema_config['source']['entity']['table_name']}_$column_name";
			$destination_alias = "{$this->schema_config['destination']['table_name']}_{$schema['destination']}";
			$row               = $this->pre_process_row( $row, $schema, $source_alias, $destination_alias );
			if ( $row[ $source_alias ] !== $row[ $destination_alias ] ) {
				if ( ! isset( $failed_ids[ $row[ $primary_key_column ] ] ) ) {
					$failed_ids[ $row[ $primary_key_column ] ] = array();
				}
				$failed_ids[ $row[ $primary_key_column ] ][] = array(
					'column'         => $column_name,
					'original_value' => $row[ $source_alias ],
					'new_value'      => $row[ $destination_alias ],
				);
			}
		}

		return $failed_ids;
	}

	/**
	 * Helper method to verify meta columns.
	 *
	 * @param array $row        Both migrated and source data for a single row.
	 * @param array $failed_ids Array of failed IDs.
	 *
	 * @return array Array of failed IDs if any, along with columns/meta_key names.
	 */
	private function verify_meta_columns( $row, $failed_ids ) {
		$primary_key_column = "{$this->schema_config['source']['entity']['table_name']}_{$this->schema_config['source']['entity']['primary_key']}";
		foreach ( $this->meta_column_mapping as $meta_key => $schema ) {
			$meta_alias        = "meta_source_{$schema['destination']}";
			$destination_alias = "{$this->schema_config['destination']['table_name']}_{$schema['destination']}";
			$row               = $this->pre_process_row( $row, $schema, $meta_alias, $destination_alias );
			if ( $row[ $meta_alias ] !== $row[ $destination_alias ] ) {
				if ( ! isset( $failed_ids[ $row[ $primary_key_column ] ] ) ) {
					$failed_ids[ $row[ $primary_key_column ] ] = array();
				}
				$failed_ids[ $row[ $primary_key_column ] ][] = array(
					'column'         => $meta_key,
					'original_value' => $row[ $meta_alias ],
					'new_value'      => $row[ $destination_alias ],
				);
			}
		}

		return $failed_ids;
	}

	/**
	 * Helper method to pre-process rows to make sure we parse the correct type.
	 *
	 * @param array  $row Both migrated and source data for a single row.
	 * @param array  $schema Column schema.
	 * @param string $alias Name of source column.
	 * @param string $destination_alias Name of destination column.
	 *
	 * @return array Processed row.
	 */
	private function pre_process_row( $row, $schema, $alias, $destination_alias ) {
		if ( ! isset( $row[ $alias ] ) ) {
			$row[ $alias ] = $this->get_type_defaults( $schema['type'] );
		}
		if ( is_null( $row[ $destination_alias ] ) ) {
			$row[ $destination_alias ] = $this->get_type_defaults( $schema['type'] );
		}
		if ( in_array( $schema['type'], array( 'int', 'decimal', 'float' ), true ) ) {
			if ( '' === $row[ $alias ] || null === $row[ $alias ] ) {
				$row[ $alias ] = 0; // $wpdb->prepare forces empty values to 0.
			}
			$row[ $alias ]             = wc_format_decimal( floatval( $row[ $alias ] ), false, true );
			$row[ $destination_alias ] = wc_format_decimal( floatval( $row[ $destination_alias ] ), false, true );
		}
		if ( 'bool' === $schema['type'] ) {
			$row[ $alias ]             = wc_string_to_bool( $row[ $alias ] );
			$row[ $destination_alias ] = wc_string_to_bool( $row[ $destination_alias ] );
		}
		if ( 'date_epoch' === $schema['type'] ) {
			if ( '' === $row[ $alias ] || null === $row[ $alias ] ) {
				$row[ $alias ] = null;
			} else {
				$row[ $alias ] = ( new \DateTime( "@{$row[ $alias ]}" ) )->format( 'Y-m-d H:i:s' );
			}
			if ( '0000-00-00 00:00:00' === $row[ $destination_alias ] ) {
				$row[ $destination_alias ] = null;
			}
		}
		return $row;
	}

	/**
	 * Helper method to get default value of a type.
	 *
	 * @param string $type Type.
	 *
	 * @return mixed Default value.
	 */
	private function get_type_defaults( $type ) {
		switch ( $type ) {
			case 'float':
			case 'int':
			case 'decimal':
				return 0;
			case 'string':
				return '';
		}
	}
}